1. Field of the Invention
In injectors for injecting fuel into combustion chambers of internal combustion engines, control parts are used that, by triggering of an actuator, can be moved into a closing and an opening position. The control parts of the injectors are guided on guide faces, by spring action in the injector body.
2. Description of the Prior Art
From German Patent Disclosure DE 198 35 494 A1, a unit fuel injector has been disclosed. It serves to deliver fuel to a combustion chamber of direct-injection internal combustion engines to build up an injection pressure and to inject the fuel, which is at high pressure, into the combustion chamber via an injection nozzle. A control part includes a control valve, which is embodied as an outward-opening valve, and a valve actuation unit for controlling the pressure buildup in the pump unit. To create a unit fuel injector with a control part that has a simple structure, is small in size, and in particular has a short response time, the valve actuation unit assigned to the unit fuel injector is embodied as a piezoelectric actuator.
From German Patent DE 37 28 817 C2, a fuel injection pump for an internal combustion engine has been disclosed. It includes a pressure part for subjecting the fuel to pressure and a nozzle part for injecting the pressurized fuel. Between the pressure part and the nozzle part, there is a control part, which includes a fuel supply line, which connects the pressure part to the nozzle part, and a cylindrical conduit whose center axis intersects the fuel supply line. One end of the conduit is embodied as a control bore that changes into an opening communicating with a fuel return conduit. A control valve member is provided in the conduit; by means of an electrical actuation device, it can be moved between an open position, in which the fuel supply and the fuel return conduit communicate via the control bore, and a closing position in which the control bore is closed. The actuating device includes an adjustable-length piezoelectric element, which is connected to a drive piston. The free end face of the drive piston is separate from and opposite a considerably smaller end face of a drive tappet that mechanically adjusts the control valve member; a passageway connecting the hollow chamber to the fuel return conduit is embodied in the drive tappet. Provided in this passageway is a check valve, which closes the passageway when the pressure in the hollow chamber exceeds the pressure in the fuel return conduit and opens the passageway when the pressure in the hollow chamber is less than the pressure in the fuel return conduit.
With the embodiment proposed by the invention, an injector design can be achieved which instead of two guide surfaces for one control part in the injector housing and two corresponding guide faces on the control part requires only one pair of guide faces on the control valve and the injector housing. The injector housing can thus be produced substantially more simply from a production standpoint and inexpensively with regard to the disposition of guide faces that are positioned exactly coaxially to one another and aligned. Only two cooperating guide faces with high demands made of the machining quality of the surfaces are required in the valve housing and on the control part movable in it, which reduces the production costs not inconsiderably.
By means of an advantageous disposition of a spring element between the guide sleeve and the control part, sealing off of the control chamber on the one hand and centering of the guide sleeve in the first diameter range of the control part on the other can be attained by prestressing the guide sleeve in the injector housing by means of the positioning force. An extremely advantageous feature from a production standpoint is that the guide sleeve need not be connected to the housing of the injector; the simple plane contact of a flat seat of the guide sleeve with a plane face of the housing of the injector is entirely adequate to seal off the control chamber upon subjection of the guide sleeve to spring force. The wall of the guide sleeve can be embodied in the simplest possible way from a production standpoint, with an inlet throttle for the control chamber volume entering the control chamber, the inlet throttle for instance being in the form of a bore that penetrates the wall of the guide sleeve.
The guide sleeve functioning as a sealing element serves as a boundary of the control chamber, on whose boundary wall toward the opening the relief opening for pressure relief is embodied by means of a triggerable actuator valve. This valve can be embodied preferably as an outlet throttle, which is actuated via an actuator, by which a closing element can be triggered. As actuator elements, electromagnets or mechanical-hydraulic boosters are also conceivable.